Multiple register clock driver loaded memory subsystem

ABSTRACT

A memory subsystem architecture that includes two register clock driver (RCD) devices to increase a number of output drivers for signaling memories of the memory subsystem is described herein. In a two RCD device implementation, first and second RCD devices may contemporaneously provide first subchannel C/A information and second subchannel C/A information, respectively, to respective first and second group of memories of the memory subsystem responsive to a common clock signal. Because each of the first and second RCD devices operate responsive to the common clock signal, operation of the first and second RCD devices may be synchronized such that all subchannel driver circuits drive respective subchannel C/A information contemporaneously.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the filing benefit of U.S. Provisional Application No. 63/047,407, filed Jul. 2, 2020. This application is incorporated by reference herein in its entirety and for all purposes.

BACKGROUND

High data reliability, high speed of memory access, lower power consumption and reduced chip/package size are features that are demanded from semiconductor memory. In some memory module implementations, a number of supportable memory die may be limited by signaling drivers on the module. For example, subchannel driver circuitry of a register clock driver may only have a physical capacity to drive command and address bus information to a fixed number of memory devices of a memory module. In addition, existing memory module architectures only support a single register clock driver chip. Thus, a register clock driver circuit may limit the number of supportable memory devices, which may limit the size of a memory module.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a memory system including a memory subsystem according to an embodiment of the present disclosure.

FIG. 2 is a block diagram of a memory system including a memory subsystem coupled to a memory controller according to an embodiment of the present disclosure.

FIGS. 3A and 3B are block diagrams of a two-stack memory package and a single-stack memory package, respectively, in accordance with embodiments of the disclosure.

FIG. 4 is a block diagram of a memory system including a memory subsystem coupled to a memory controller according to an embodiment of the present disclosure.

FIG. 5 is a block diagram of a semiconductor device according to an embodiment of the present disclosure.

FIG. 6 is a flow diagram of a method for dual register clock driver loading of a memory subsystem according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

This disclosure describes a memory subsystem architecture that includes two register clock driver (RCD) devices to increase the number of output drivers for signaling memories of the memory subsystem to provide an ability to support a greater number of memories as compared with implementations that use only single RCD device. In some architectures, for a single channel, a memory controller (e.g., or host, central processor unit, one or more other processor units, etc.) may provide respective command and address (C/A) information over two independent subchannels (e.g., using different respective sets of C/A signal lines) in parallel, along with a single clock signal used to synchronize timing of the two subchannels such that the respective C/A information for each subchannel is provided to a respective group (e.g., a memory rank, a memory package, or some other grouping) of memories (e.g., die, devices, etc.) contemporaneously.

Thus, in a two RCD device implementation, the clock signal may be split (e.g., via clock tee) such that the clock signal is provided to the two RCD devices contemporaneously. The clock tee may be arranged to reduce likelihood of asynchronous timing between the two RCD devices. In an example, first and second RCD devices may be configured to provide first subchannel C/A information and second subchannel C/A information, respectively, to respective first and second group of memories of the memory subsystem. Each of the first and second RCD devices may include dual (e.g., A and B), independent subchannel driver circuits configured to provide respective subchannel C/A information to a respective subset of the respective group of memories. For example, in response to the clock signal, the first subchannel driver circuit of the first RCD device may provide the first subchannel C/A information to a first and second subsets of a first group of memories contemporaneously with provision of the first subchannel C/A information to a third and fourth subsets of the first group of memories by the second subchannel driver circuit of the first RCD device. The first and second subchannel driver circuits of the second RCD device may perform a similar operation to contemporaneously provide the second subchannel C/A information to respective subsets of the second group of memories in response to the clock signal. Because each of the first and second RCD devices operate responsive to the common clock signal, operation of the first and second RCD devices may be synchronized such that all subchannel driver circuits drive respective subchannel C/A information contemporaneously. As previously mentioned, an ability to support more than one RCD device on a memory subsystem may increase a number of output drivers, which may, correspondingly provide support for an increased number of memories on the memory subsystem as compared with single RCD device memory subsystem implementations.

FIG. 1 is a block diagram of a memory system 100 including a memory subsystem 104 according to an embodiment of the present disclosure. The memory subsystem 104 may be coupled to C/A A bus, C/A B bus, and a clock bus providing a clock signal CLK to receive command and address information form a memory controller (e.g., or a host, central processor unit, one or more other processor units or controllers, a DRAM controller, etc.) (not shown) of the memory system 100. The memory subsystem 104 may include a memory package 110(1) and a memory package 110(2). The memory subsystem 104 may include a memory module, such as a dual, inline memory module (DIMM) (e.g., a registered DIMM, a load reduction DIMM (LRDIMM), a micro DIMM, non-volatile DIMM (NVDIMM) (e.g., including non-volatile memory and a controller (not shown)), or any other type of DIMM). In some examples, the memory subsystem 104 may include a soldered memory subsystem other than a memory module and/or a DIMM.

The memory package 110(1) may include a register clock driver circuit 112(1) coupled to memories 114(1) and the memory package 110(2) may include a register clock driver circuit 112(2) coupled to memories 114(2). The register clock driver circuit 112(1) may be configured to receive first subchannel C/A information from the C/A A bus and the CLK signal and the register clock driver circuit 112(2) may be configured to receive second subchannel C/A information from the C/A B bus and the CLK signal. The first and second subchannel C/A information may correspond to C/A information for a single channel. The first subchannel C/A information and the second subchannel C/A information may include memory access commands and addresses, chip select signals, etc., corresponding to first and second subchannels, respectively. The first and/or second subchannel C/A information may also include information to configure the memory subsystem 104 and/or components of the memory package 110(1) and/or the memory package 110(2). The register clock driver circuit 112(1) may provide the first subchannel C/A information to each of C/A A1-A4 buses in parallel responsive to the CLK signal and the register clock driver circuit 112(2) may provide the second subchannel C/A information to each of C/A B1-B4 buses in parallel responsive to the CLK signal.

Each memory of the memories 114(1) may be coupled to a respective one of C/A A1-A4 buses to receive first subchannel C/A information and each memory of the memories 114(2) may be coupled to a respective one of C/A B1-B4 buses to receive second subchannel C/A information. Each memory of the memories 114(1) may also be coupled to a respective data bus to receive write data from and to provide read data to the memory controller responsive to the first subchannel C/A information. Additionally, each memory of the memories 114(2) may be coupled to a respective data bus to receive write data from and to provide read data to the memory controller responsive to the second subchannel C/A information. The memories 114(1) and/or the memories 114(2) may each include one or more memory devices, packages, and/or memory die. In some examples, the one or more memory devices or packages may each include one or more memory die stacks. The memories 114(1) and/or the memories 114(2) may each include dynamic, random-access memory (DRAM) (e.g., double data rate (DDR) 4 DRAM, DDR5 DRAM, DDR6 DRAM, etc.), in some examples.

In operation, for a given communication channel, a memory controller of the memory system 100 may contemporaneously provide respective first and second subchannel C/A information over two independent subchannels via the C/A A bus and C/A B bus, respectively, along with a single clock signal used to synchronize timing of the two subchannels to the memory subsystem 104. In some examples, the memory subsystem 104 and/or one or both of the memory package 110(1) and the memory package 110(2) may further include a control plane hub (e.g., device or chip) (not shown) to provide control plane communication between components of the memory subsystem 104 and/or one or both of the memory package 110(1) and the memory package 110(2), such as the register clock driver circuit 112(1), the register clock driver circuit 112(2), thermal sensors (not shown), power management integrated circuits (not shown), etc., or any combination thereof based on at least one of the first subchannel C/A information from the C/A A bus or the second subchannel C/A information from the C/A B bus. The control plane communications may be used to configure parameters of the components of the memory subsystem 104 and/or one or both of the memory package 110(1) and the memory package 110(2), such as voltage levels, clock timing characteristics, modes of operation, etc.

The memory package 110(1) is configured to receive and respond to the first subchannel C/A information to receive and store write data at and provide read data from the memories 114(1) to the memory controller via the respective data bus and the memory package 110(2) is configured to receive and respond to the second subchannel C/A information to receive and store write data at and provide read data from the memories 114(2) to the memory controller via the respective data bus.

The register clock driver circuit 112(1) and the register clock driver circuit 112(2) may each be configured to drive the first and second subchannel C/A information received from the C/A A bus and the C/A B bus, respectively, to the C/A A1-A4 buses and the C/A B1-B4 buses, respectively, responsive to the CLK signal. The CLK signal may be split (e.g., via clock tee) such that is routed to and received at the register clock driver circuit 112(1) and the register clock driver circuit 112(2) contemporaneously. The clock tee may be arranged (e.g., impedance matched, trace length and shape, etc.) to reduce likelihood of timing differences at the register clock driver circuit 112(1) and at the register clock driver circuit 112(2). Each of the register clock driver circuit 112(1) and the register clock driver circuit 112(2) may include dual (e.g., A and B), independent subchannel driver circuits that are each configured to drive the respective subchannel C/A information to a respective two of the C/A A1-A4 buses or a respective two of the C/A B1-B4 buses. For example, in response to the CLK signal, the first subchannel driver circuit of the register clock driver circuit 112(1) may provide the first subchannel C/A information to the C/A A1-A2 buses and the second subchannel driver circuit of the register clock driver circuit 112(1) may provide the first subchannel C/A information to the C/A A3-A4 buses. The subchannel driver circuits of the register clock driver circuit 112(2) may each similarly provide the second subchannel C/A information to a respective two of the C/A B1-B4 buses responsive to the CLK signal.

The memories 114(1) may be divided into four subsets, with the memories of each subset coupled to an individual one of the C/A A1-A4 buses to receive the first subchannel C/A information. Similarly, the memories 114(2) may be divided into four subsets, with the memories of each subset coupled to an individual one of the C/A B1-B4 buses to receive the second subchannel C/A information. One or more of the memories 114(1) may receive write data from or provide read data to the memory controller via the respective data bus, as well as perform other operations, responsive to the first subchannel C/A information. Similarly, one or more of the memories 114(2) may receive write data from or provide read data to the memory controller via the respective data bus, as well as perform other operations, responsive to the second subchannel C/A information.

It is appreciated that, without departing from the scope of the disclosure, the memory subsystem 104 could be scaled to include more than two memory packages, more than two RCD circuits, and/or more than two groups of memories, such as to support additional subchannels (e.g., supported by additional C/A buses and/or CLK signals). It is also appreciated that each of the register clock driver circuit 112(1) and the register clock driver circuit 112(2) may be configured with additional driver circuits to support more than four independent C/A buses. An ability to support more than one RCD circuit on the memory subsystem 104 may increase a number of output drivers, which may, correspondingly provide support for an increased number of memories on the memory subsystem 104 as compared with single RCD device memory subsystem implementations.

FIG. 2 is a block diagram of a memory system 200 including a memory subsystem 204 coupled to a memory controller 202 according to an embodiment of the present disclosure. The memory subsystem 204 may be coupled to C/A A bus, C/A B bus, and a clock signal CLK driven by the memory controller 202. The memory controller 202 may include a host, central processor unit, one or more other processor units or controllers, a DRAM controller, etc. The memory subsystem 204 may include a printed circuit board 205 with traces to support signal lines for the C/A A bus, the C/A B bus, and the CLK signal, and may include infrastructure to support installation of a memory package 210(1) and a memory package 210(2). In some examples, the printed circuit board 205 may include a memory module printed circuit board, such as a DIMM printed circuit board. In other examples, the printed circuit board 205 includes a motherboard printed circuit board, or any other type of printed circuit board. In some examples, the memory subsystem 204 may include memory module, such as a DIMM (e.g., including a registered DIMM, a LRDIMM, a micro DIMM, a NVDIMM, or any other type of DIMM). In some examples, the memory subsystem 204 may include a soldered memory subsystem other than a memory module and/or a DIMM. The memory subsystem 104 of FIG. 1 may implement the memory subsystem 204, in some examples.

The memory package 210(1) may include a register clock driver circuit 212(1) coupled to memories 214(1) and the memory package 210(2) may include a register clock driver circuit 212(2) coupled to memories 214(2). The register clock driver circuit 212(1) may be configured to receive first subchannel C/A information from the C/A A bus and the CLK signal and the register clock driver circuit 212(2) may be configured to receive second subchannel C/A information from the C/A B bus and the CLK signal. The first and second subchannel C/A information may correspond to C/A information for a single channel. The first subchannel C/A information and the second subchannel C/A information may include memory access commands and addresses, chip select signals, etc., corresponding to first and second subchannels, respectively. The first and/or second subchannel C/A information may also include information to configure the memory subsystem 204 and/or components of the memory package 210(1) and/or the memory package 210(2). The register clock driver circuit 212(1) may provide the first subchannel C/A information to each of C/A A1-A4 buses in parallel (e.g., contemporaneously) responsive to the CLK signal and the register clock driver circuit 212(2) may provide the second subchannel C/A information to each of C/A B1-B4 buses in parallel responsive to the CLK signal.

The register clock driver circuit 212(1) may include a first driver circuit 240(1) and a second driver circuit 242(1) that are each configured to receive the first subchannel C/A information in parallel (e.g., contemporaneously) from the C/A A bus via a 232(1) and a clock driver circuit 244(1) configured to receive the CLK signal. Responsive to the CLK signal driven from the clock driver circuit 244(1), the first driver circuit 240(1) may be configured to drive the first subchannel C/A information to the C/A A1-A2 buses and the second driver circuit 242(1) may be configured to drive the first subchannel C/A information to the C/A A3-A4 buses.

Similarly, the register clock driver circuit 212(2) may include a first driver circuit 240(2) and a second driver circuit 242(2) that are each configured to receive the second subchannel C/A information in parallel (e.g., contemporaneously) from the C/A B bus via a 232(2) and a clock driver circuit 244(2) configured to receive the CLK signal. Responsive to the CLK signal driven from the clock driver circuit 244(1), the first driver circuit 240(1) may be configured to drive the second subchannel C/A information to the C/A B1-B2 buses and the second driver circuit 242(1) may be configured to drive the second subchannel C/A information to the C/A B3-B4 buses.

Each memory of the memories 214(1) may be coupled to a respective one of C/A A1-A4 buses to receive first subchannel C/A information and each memory of the memories 214(2) may be coupled to a respective one of C/A B1-B4 buses to receive second subchannel C/A information. Each memory of the memories 214(1) may also be coupled to a respective data bus to receive write data from and to provide read data to the memory controller responsive to the first subchannel C/A information. Additionally, each memory of the memories 214(2) may be coupled to a respective data bus to receive write data from and to provide read data to the memory controller responsive to the second subchannel C/A information. The memories 214(1) and/or the memories 214(2) may each include one or more memory devices, packages, and/or memory die. In some examples, the one or more memory devices or packages may each include one or more memory die stacks. The memories 214(1) and/or the memories 214(2) may each include dynamic, random-access memory (DRAM) (e.g., double data rate (DDR) 4 DRAM, DDR5 DRAM, DDR6 DRAM, etc.), in some examples.

In operation, for a given communication channel, C/A A and C/A B drivers of the memory controller 202 may contemporaneously provide respective first and second subchannel C/A information over two independent subchannels via the C/A A bus and C/A B bus, respectively, along with a CLK driver to provide a single clock signal over a clock signal line that is used to synchronize timing of the two subchannels to the memory subsystem 204. In some examples, a logic chip on the 206 and/or one or both of the memory package 210(1) and the memory package 210(2) may further include a control plane hub (e.g., device or chip) (not shown) to provide control plane communication between components of the memory subsystem 204 and/or one or both of the memory package 210(1) and the memory package 210(2), such as the register clock driver circuit 212(1), the register clock driver circuit 212(2), thermal sensors (not shown), power management integrated circuits (not shown), etc., or any combination thereof based on at least one of the first subchannel C/A information from the C/A A bus or the second subchannel C/A information from the C/A B bus. The control plane communications may be used to configure parameters of the components of the memory subsystem 204 and/or one or both of the memory package 210(1) and the memory package 210(2), such as voltage levels, clock timing characteristics, modes of operation, etc.

The memory package 210(1) is configured to receive and respond to the first subchannel C/A information to receive and store write data at and provide read data from the memories 214(1) to the memory controller via the respective data bus and the memory package 210(2) is configured to receive and respond to the second subchannel C/A information to receive and store write data at and provide read data from the memories 214(2) to the memory controller via the respective data bus.

The register clock driver circuit 212(1) and the register clock driver circuit 212(2) may each be configured to drive the first and second subchannel C/A information received from the C/A A bus and the C/A B bus, respectively, to the C/A A1-A4 buses and the C/A B1-B4 buses, respectively, responsive to the CLK signal. The CLK signal may be split (e.g., via clock tee) such that is routed to and received at the register clock driver circuit 212(1) and the register clock driver circuit 212(2) contemporaneously. The clock tee may be arranged (e.g., impedance matched, trace length and shape, etc.) to reduce likelihood of timing differences the register clock driver circuit 212(1) and the register clock driver circuit 212(2).

The first driver circuit 240(1) and the second driver circuit 242(1) of the register clock driver circuit 212(1) may each receive the first subchannel C/A information in parallel (e.g., contemporaneously) from the C/A A bus and the clock driver circuit 244(1) may receive the CLK signal. The C/A A bus may be split via a tee 230(1) to provide the first subchannel C/A information to each of the first driver circuit 240(1) and the second driver circuit 242(1). Responsive to the CLK signal driven from the clock driver circuit 244(1), the first driver circuit 240(1) may drive the first subchannel C/A information to the C/A A1-A2 buses and the second driver circuit 242(1) may drive the first subchannel C/A information to the C/A A3-A4 buses.

The first driver circuit 240(2) and the second driver circuit 242(2) of the register clock driver circuit 212(2) may receive the second subchannel C/A information in parallel (e.g., contemporaneously) from the C/A B bus and the clock driver circuit 244(2) may receive the CLK signal. The C/A B bus may be split via a tee 230(2) to provide the first subchannel C/A information to each of the first driver circuit 240(2) and the second driver circuit 242(2). Responsive to the CLK signal driven from the clock driver circuit 244(1), the first driver circuit 240(1) may drive the second subchannel C/A information to the C/A B1-B2 buses and the second driver circuit 242(1) may drive the second subchannel C/A information to the C/A B3-B4 buses. The second driver circuit 242(1), the clock driver circuit 244(1), the second driver circuit 242(2), and the clock driver circuit 244(2) may all operation in a synchronized manner with timing based on the common CLK signal.

The memories 214(1) may be divided into four subsets, with the memories of each subset coupled to an individual one of the C/A A1-A4 buses to receive the first subchannel C/A information. Similarly, the memories 214(2) may be divided into four subsets, with the memories of each subset coupled to an individual one of the C/A B1-B4 buses to receive the second subchannel C/A information. One or more of the memories 214(1) may receive write data from or provide read data to the memory controller via the respective data bus, as well as perform other operations, responsive to the first subchannel C/A information. Similarly, one or more of the memories 214(2) may receive write data from or provide read data to the memory controller via the respective data bus, as well as perform other operations, responsive to the second subchannel C/A information.

It is appreciated that, without departing from the scope of the disclosure, the memory subsystem 204 could be scaled to include more than two memory packages, more than two RCD circuits, and/or more than two groups of memories, such as to support additional subchannels (e.g., supported by additional C/A buses and/or CLK signals). It is also appreciated that each of the register clock driver circuit 212(1) and the register clock driver circuit 212(2) may be configured with additional driver circuits to support more than four independent C/A buses. An ability to support more than one RCD circuit on the memory subsystem 204 may increase a number of output drivers, which may, correspondingly provide support for an increased number of memories on the memory subsystem 204 as compared with single RCD device memory subsystem implementations.

FIGS. 3A and 3B are block diagrams of a dual-stack memory package 310 and a single-stack memory package 311, respectively, in accordance with embodiments of the disclosure. The memory package 110(1) and/or the memory package 110(2) of FIG. 1 and/or the memory package 210(1) and/or the memory package 210(2) of FIG. 2 may implement the dual-stack memory package 310 and/or the single-stack memory package 311, in some examples.

FIG. 3A includes a side view 301 and a top (e.g., plan) view 302 of the dual-stack memory package 310. The side view 301 depicts the memory package 310 from the perspective of the side 305 (i.e., right side of the top view 302) of the memory package 310 in the FIG. 3A. The dual-stack memory package 310 may include register clock driver circuit 312 and a memory 314. The register clock driver circuit 312 may be configured to perform operations as described with reference to the register clock driver circuit 112(1) or the register clock driver circuit 112(2) of FIG. 1 and/or the register clock driver circuit 212(1) or the register clock driver circuit 212(2) of FIG. 2. The dual-stack memory package 310 may be coupled to a C/A bus (e.g., one of the C/A A1-A4 buses or one of the C/A B1-B4 buses of FIGS. 1 and/or 2) to receive respective subchannel C/A information, to a clock signal line to receive the clock signal CLK (e.g., the CLK signal of FIGS. 1 and/or 2), and to a respective data bus to receive write data and to provide read data.

The memory 314 may include a die stack 342(1) and a die stack 342(2) that each include 10 of the memory die 360 stacked in a shingle or cascade stacked arrangement (e.g., each of the memory die 360 is offset horizontally from adjacent ones of the memory die 360). Each of the memory die 360 may include a DRAM architecture, such as DDR4 DRAM, DDR5 DRAM, DDR6 DRAM, etc.), in some examples. Each of the memory die 360 of the die stack 342(1) and the die stack 342(2) may be coupled to other circuitry to perform memory access operations via respective wire bonds 350. It is appreciated that the die stack 342(1) and the die stack 342(2) may include more or fewer than 10 of the memory die 360 without departing from the scope of the disclosure. It is also appreciated that the die stack 342(1) may include a different number of the memory die 360 than the die stack 342(2), in some examples. It is also appreciated that the die stack 342(1) and/or the die stack 342(2) may be arranged to use other stacking and connection implementations, such as a 3D through-silicon via stack, without departing from the scope of the disclosure.

In some examples, the dual-stack memory package 310 may further include a control plane hub (e.g., device or chip) (not shown) to provide control plane communication between components of the dual-stack memory package 310, such as the register clock driver circuit 312, thermal sensors (not shown), power management integrated circuits (not shown), etc., or any combination thereof based on the respective subchannel C/A information from the respective C/A bus. The control plane communications may be used to configure parameters of the components of the dual-stack memory package 310, such as voltage levels, clock timing characteristics, modes of operation, etc.

FIG. 3B includes a side view 303 and a top (e.g., plan) view 304 of the single-stack memory package 311. The side view 303 depicts the memory package 311 from the perspective of the side 306 (i.e., right side of the top view 304) of the memory package 310 in the FIG. 3B. The single-stack memory package 311 may include register clock driver circuit 312 and a memory 315. The register clock driver circuit 312 may be configured to perform operations as described with reference to the register clock driver circuit 112(1) or the register clock driver circuit 112(2) of FIG. 1 and/or the register clock driver circuit 212(1) or the register clock driver circuit 212(2) of FIG. 2. The single-stack memory package 311 may be coupled to a C/A bus (e.g., one of the C/A A1-A4 buses or one of the C/A B1-B4 buses of FIGS. 1 and/or 2) to receive respective subchannel C/A information, to a clock signal line to receive the clock signal CLK (e.g., the CLK signal of FIGS. 1 and/or 2), and to a respective data bus to receive write data and to provide read data.

The memory 315 may include a die stack 343 that includes 20 of the memory die 360 stacked in a shingle or cascade stacked arrangement (e.g., each of the memory die 360 is offset horizontally from adjacent ones of the memory die 360). Each of the memory die 360 of the die stack 343 may be coupled to other circuitry to perform memory access operations via respective wire bonds 350. It is appreciated that the die stack 343 may include more or fewer than 20 of the memory die 360 without departing from the scope of the disclosure. It is also appreciated that the die stack 343 may be arranged to use other stacking and connection implementations, such as a 3D through-silicon via stack, without departing from the scope of the disclosure.

In some examples, the dual-stack memory package 310 may further include a control plane hub (e.g., device or chip) (not shown) to provide control plane communication between components of the single-stack memory package 311, such as the register clock driver circuit 312, thermal sensors (not shown), power management integrated circuits (not shown), etc., or any combination thereof based on the respective subchannel C/A information from the respective C/A bus. The control plane communications may be used to configure parameters of the components of the single-stack memory package 311, such as voltage levels, clock timing characteristics, modes of operation, etc.

FIG. 4 is a block diagram of a memory system 400 including a memory subsystem 404 coupled to a memory controller 402 according to an embodiment of the present disclosure. The memory subsystem 404 may include a memory module, such as a DIMM (e.g., a registered DIMM, a load reduction DIMM (LRDIMM), a micro DIMM, a NVDIMM, or any other type of DIMM). In some examples, the memory subsystem 404 may include a soldered memory subsystem other than a memory module and/or a DIMM. The memory subsystem 104 of FIG. 1 and/or the memory subsystem 204 of FIG. 2 may implement the memory subsystem 404, in some examples.

The memory subsystem 404 may be configured to communicate with a memory controller 402 to perform memory access operations based on a clock signal CLK, first subchannel C/A information from a C/A/A bus, second subchannel C/A information from a C/A/B bus, and/or data transferred via signals over respective data buses. In some examples, the memory controller 402 may a C/A A bus driver 462 configured to drive first subchannel C/A information from a C/A/A bus, a C/A B bus driver 464 configured to drive second subchannel C/A information from a C/A/B bus, and a clock driver 466 configured to drive the CLK signal over the clock signal line. The memory controller 402 may further include drivers and receivers (not shown) coupled to the respective data buses to provide write data and to receive read data, respectively.

The memory subsystem 404 may include memories 414(1)-(8) coupled to Register clock driver circuit 412(1) and memories 414(9)-(16) coupled to Register clock driver circuit 412(2). The register clock driver circuit 412(1) may be configured to receive first subchannel C/A information from the C/A A bus and the CLK signal and the register clock driver circuit 412(2) may be configured to receive second subchannel C/A information from the C/A B bus and the CLK signal. The first and second subchannel C/A information may correspond to C/A information for a single channel. The first subchannel C/A information and the second subchannel C/A information may include memory access commands and addresses, chip select signals, etc., corresponding to first and second subchannels, respectively. The first and/or second subchannel C/A information may also include information to configure the memory subsystem 404 and/or components of the memory subsystem 404. The register clock driver circuit 412(1) may provide the first subchannel C/A information to each of C/A A1-A2 buses in parallel responsive to the CLK signal and the register clock driver circuit 412(2) may provide the second subchannel C/A information to each of C/A B1-B2 buses in parallel responsive to the CLK signal. It is appreciated that the memory subsystem 404 of FIG. 4 may include a dual side memory module, where an opposite side (not shown) of the memory subsystem 404 includes additional memories arranged similar to the memories 414(0)-(15) and that the register clock driver circuit 412(1) and the register clock driver circuit 412(2) may provide the first and second subchannel C/A information, respectively, on additional C/A A3-A4 buses and C/A B3-B4 buses, respectively, without departing from the scope of the disclosure.

In some examples, the memories 414(1)-(16) may all be the same type of memory. In other examples, the memories 414(1)-(16) may be a mix of different types of memories. In some examples, the memories 414(1)-(16) may implement in the memories 114(1) and/or the memories 114(2) of FIG. 1, the memories 214(1) and/or the memories 214(2) of FIG. 1, the memory 314 and/or one or more of the memory die 360 of FIG. 3A, the memory 315 and/or one or more of the memory die 360 of FIG. 3B, or any combination thereof. Although the memory module 404 shown in FIG. 4 having 16 memories 414(1)-(16), more or fewer memories may be used in other embodiments. In some examples, the memory subsystem 404 may include an additional memory (not shown) that is used for error correcting code (ECC) storage. Each of the memories 414(1)-(16) may include one or more memory devices, packages, and/or memory die. In some examples, the one or more memory devices or packages may each include one or more memory die stacks. The memories 414(1)-(16) may include DRAM architecture, such as DDR4 DRAM, DDR5 DRAM, DDR6 DRAM, etc.

Each of the memories 414(1)-(4) may be coupled to the C/A A1 bus and each of the memories 414(5)-(8) may be coupled to the C/A A2 bus to receive first subchannel C/A information. Each of the memories 414(9)-(12) may be coupled to the C/A B1 bus and each of the memories 414(13)-(16) may be coupled to the C/A B2 bus to receive second subchannel C/A information. Each of the memories 414(1)-(16) may also be coupled to a respective data bus to receive write data from and to provide read data to the memory controller 202 responsive to the first subchannel C/A information or the second subchannel C/A information.

In some embodiments, the memories 414(1)-(16) may be organized into different physical ranks and/or may be included on one or both sides of the memory subsystem 404. In some embodiments, there may be 4, 8, 16, or more memories per physical rank, and one or more physical ranks in the memory subsystem 404. For example, the memory subsystem 404 may include a first physical rank on a first side of the memory subsystem 404 (e.g., the 16 memories 414(1)-(16)), and a second physical rank on a back side of the memory subsystem 404 (e.g., 16 more memories on a reverse side of the memory subsystem 404).

In operation, for a given communication channel, the C/A A bus driver 462 and the C/A B bus driver 464 of the 402 may contemporaneously provide respective first and second subchannel C/A information over two independent subchannels via the C/A A bus and C/A B bus, respectively, along with a clock driver 466 to provide a single clock signal over a clock signal line that is used to synchronize timing of the two subchannels to the memory subsystem 404. In some examples, the memory subsystem 404 may further include a control plane hub (e.g., device or chip) (not shown) to provide control plane communication between components of the memory subsystem 404, such as the register clock driver circuit 412(1), the register clock driver circuit 412(2), thermal sensors (not shown), power management integrated circuits (not shown), etc., or any combination thereof based on at least one of the first subchannel C/A information from the C/A A bus or the second subchannel C/A information from the C/A B bus. The control plane communications may be used to configure parameters of the components of the memory subsystem 404, such as voltage levels, clock timing characteristics, modes of operation, etc.

The register clock driver circuit 412(1) and the register clock driver circuit 412(2) may each be configured to drive the first and second subchannel C/A information received from the C/A A bus and the C/A B bus, respectively, to the C/A A1-A2 buses and the C/A B1-B2 buses, respectively, responsive to the CLK signal. The CLK signal may be split (e.g., via clock tee) such that is routed to and received at the register clock driver circuit 412(1) and the register clock driver circuit 412(2) contemporaneously. The clock tee may be arranged (e.g., impedance matched, trace length and shape, etc.) to reduce likelihood of timing differences the register clock driver circuit 212(1) and the register clock driver circuit 212(2).

Each of the memories 414(1)-(4) may receive the first subchannel C/A information via the C/A A1 bus and each of the memories 414(5)-(8) may receive the first subchannel C/A information via the C/A A2 bus. One or more of the memories 414(1)-(8) may perform memory access operations responsive to the first subchannel C/A information to receive data from and provide data to the respective data buses in communication with the memory controller 402.

Each of the memories 414(9)-(12) may receive the second subchannel C/A information via the C/A B1 bus and each of the memories 414(13)-(16) may receive the second subchannel C/A information via the C/A B2 bus. One or more of the memories 414(9)-(16) may perform memory access operations responsive to the second subchannel C/A information to receive data from and provide data to the respective data buses in communication with the memory controller 402.

It is appreciated that, without departing from the scope of the disclosure, the memory subsystem 404 could be scaled to include more than 16 (or 32) memories, more than two register clock driver circuits, and/or more than two groups of memories, such as to support additional subchannels (e.g., supported by additional C/A buses and/or CLK signals). It is also appreciated that each of the register clock driver circuit 412(1) and the register clock driver circuit 412(2) may be configured with additional driver circuits to support more than four independent C/A buses. An ability to support more than one register clock driver circuit on the memory subsystem 404 may increase a number of output drivers, which may, correspondingly provide support for an increased number of memories on the memory subsystem 404 as compared with single RCD device memory module implementations.

FIG. 5 is a block diagram of a semiconductor device 500 according to at least one embodiment of the disclosure. The semiconductor device 500 may be a semiconductor memory device, such as DRAM device (e.g., double data rate (DDR) 4 DRAM, DDR5 DRAM, DDR6 DRAM, etc.) integrated on a single semiconductor chip. The example device 500 of FIG. 5 may include a memory package such as the stack of memory dies positioned on a substrate 523, which may function as (and may be referred to) as an interface. Although certain components are shown in the dies of the stack of memory dies, and certain components on the substrate 523, other arrangement of the components of the device 500 between the stack and the substrate 523 are possible in other example embodiments. In some embodiments, the device 500 may include multiple stacks of memory dies. In other embodiments, the stack of memory dies may include a single memory die. The memory package 110(1) and/or the memory package 110(2) of FIG. 1, the memory package 210(1) and/or the memory package 210(2) of FIG. 2, the dual-stack memory package 310 and/or either or both of the die stack 342(1) and the die stack 342(2) of FIG. 3A, the single-stack memory package 311 and/or the die stack 343 of FIG. 3B, any of the memories register clock driver circuit 412(1)-(16) of FIG. 4, or any combination thereof, may implement the semiconductor device 500, in some examples.

For brevity and clarity of illustration, only the components of one memory die in the stack stack of memory dies are shown in FIG. 5. Generally, the different dies of the stack of memory dies may each have similar components to each other. In some embodiments, each die of the stack of memory dies may be physically identical to each other. The substrate 523 may act as an interface, and may send and receive information (e.g., data, commands) to and from the outside, while the memory dies in the stack of memory dies communicate with components of the substrate 523. As described herein, commands and other signals sent by the substrate 523 may be sent to all dies in the stack of memory dies or may be separately addressed to individual dies of the stack of memory dies.

The semiconductor device 500 includes a memory array 518. The memory array 518 may be positioned in a die of the stack of memory dies. The memory array 518 is shown as including a plurality of memory banks. In the embodiment of FIG. 5, the memory array 518 is shown as including N+1 memory banks BANK0-N, where N is any integer value, such as 2, 4, 8, 16, 32, etc. Each of the memory banks BANK0-N may include a plurality of word lines WL, a plurality of bit lines BL and /BL, and a plurality of memory cells MC arranged at intersections of the plurality of word lines WL and the plurality of bit lines BL and /BL. The selection of the word line WL is performed by a row decoder 508 and the selection of the bit lines BL and /BL is performed by a column decoder 510. The row and column decoders 508 and 510 may also be positioned in the memory dies of the stack of memory dies. In the embodiment of FIG. 5, the row decoder 508 includes a respective row decoder for each memory bank and the column decoder 510 includes a respective column decoder for each memory bank. The bit lines BL and /BL are coupled to a respective sense amplifier (SAMP). Read data from the bit line BL or /BL is amplified by the sense amplifier SAMP, and transferred to read/write amplifiers 520 over complementary local data lines (LIOT/B), transfer gate (TG), and complementary main data lines (MIOT/B). Conversely, write data outputted from the read/write amplifiers 520 is transferred to the sense amplifier SAMP over the complementary main data lines MIOT/B, the transfer gate TG, and the complementary local data lines LIOT/B, and written in the memory cell MC coupled to the bit line BL or /BL.

The semiconductor device 500 may employ a plurality of external terminals that include command and address (C/A) terminals coupled to a command and address bus to receive commands and addresses, and a CS signal, clock terminals to receive clocks CK and /CK, data terminals DQ to receive and provide data (e.g., via a multi-channel data bus), and power supply terminals to receive power supply potentials VDD, VSS, VDDQ, and VSSQ. The external terminals may be positioned on the substrate 523.

The clock terminals are supplied with external clocks CK and /CK that are provided to an input circuit 514. The external clocks may be complementary. The input circuit 514 generates an internal clock ICLK based on the CK and /CK clocks. The ICLK clock is provided to the command decoder 510 and to an internal clock generator 512. The internal clock generator 512 provides various internal clocks LCLK based on the ICLK clock. The LCLK clocks may be used for timing operation of various internal circuits. The internal data clocks LCLK are provided to the input/output circuit 522 to time operation of circuits included in the input/output circuit 522, for example, to data receivers to time the receipt of write data.

The C/A terminals may be supplied with memory addresses. The memory addresses supplied to the C/A terminals are transferred, via a command/address input circuit 502, to an address decoder 504. The address decoder 504 receives the address and supplies a decoded row address XADD to the row decoder 508 and supplies a decoded column address YADD to the column decoder 510. The address decoder 504 may also supply a decoded bank address BADD, which may indicate the bank of the memory array 518 containing the decoded row address XADD and column address YADD. In some embodiments, the address decoder 504 may also indicate a particular memory die of the stack of memory dies for activation. The C/A terminals may be supplied with commands Examples of commands include timing commands for controlling the timing of various operations, access commands for accessing the memory, such as read commands for performing read operations and write commands for performing write operations, as well as other commands and operations. The access commands may be associated with one or more row address XADD, column address YADD, and bank address BADD to indicate the memory cell(s) to be accessed.

The commands may be provided as internal command signals to a command decoder 506 via the command/address input circuit 502. The command decoder 506 includes circuits to decode the internal command signals to generate various internal signals and commands for performing operations. For example, the command decoder 506 may provide a row command signal to select a word line and a column command signal to select a bit line.

The semiconductor device 500 may receive an access command which is a read command. When a read command is received, and a bank address, a row address and a column address (and optional die address) are timely supplied with the read command, read data is read from memory cells in the memory array 518 corresponding to the row address and column address. The read command is received by the command decoder 506, which provides internal commands so that read data from the memory array 518 is provided to the read/write amplifiers 520. The read data is output to outside from the data terminals DQ via the input/output circuit 522.

The semiconductor device 500 may receive an access command which is a write command. When the write command is received, and a bank address, a row address and a column address (and optional die address) are timely supplied with the write command, write data supplied to the data terminals DQ is written to a memory cells in the memory array 518 corresponding to the row address and column address. The write command is received by the command decoder 506, which provides internal commands so that the write data is received by data receivers in the input/output circuit 522. Write clocks may also be provided to the external clock terminals for timing the receipt of the write data by the data receivers of the input/output circuit 522. The write data is supplied via the input/output circuit 522 to the read/write amplifiers 520, and by the read/write amplifiers 520 to the memory array 518 to be written into the memory cell MC.

The power supply terminals are supplied with power supply potentials VDD and VSS. The power supply potentials VDD and VSS are supplied to an internal voltage generator circuit 524. The internal voltage generator circuit 524 generates various internal potentials VPP, VOD, VARY, VPERI, and the like based on the power supply potentials VDD and VSS supplied to the power supply terminals. The internal potential VPP is mainly used in the row decoder 508, the internal potentials VOD and VARY are mainly used in the sense amplifiers SAMP included in the memory array 518, and the internal potential VPERI is used in many peripheral circuit blocks.

The power supply terminals are also supplied with power supply potentials VDDQ and VSSQ. The power supply potentials VDDQ and VSSQ are supplied to the input/output circuit 522. The power supply potentials VDDQ and VSSQ supplied to the power supply terminals may be the same potentials as the power supply potentials VDD and VSS supplied to the power supply terminals in an embodiment of the disclosure. The power supply potentials VDDQ and VSSQ supplied to the power supply terminals may be different potentials from the power supply potentials VDD and VSS supplied to the power supply terminals in another embodiment of the disclosure. The power supply potentials VDDQ and VSSQ supplied to the power supply terminals are used for the input/output circuit 522 so that power supply noise generated by the input/output circuit 522 does not propagate to the other circuit blocks.

FIG. 6 is a flow diagram of a method 600 for dual register clock driver loading of a memory subsystem according to an embodiment of the present disclosure. The method 600 may be performed, at least in part, by the memory subsystem 104 of FIG. 1, the memory subsystem 204 of FIG. 2, the dual-stack memory package 310 of FIG. 3A, the single-stack memory package 311 of FIG. 3B, the memory subsystem 404 of FIG. 4, or any combination thereof.

The method 600 may include receiving, at a first register clock driver of a memory subsystem, first subchannel command and address information corresponding to a channel via a first command and address bus and a clock signal, at 610. The method 600 may include receiving, at a second register clock driver of the memory subsystem, second subchannel command and address information corresponding to the channel via a second command and address bus and the clock signal, at 620. The first and/or second register clock drivers may include the register clock driver circuit 112(1) and/or the register clock driver circuit 112(2) of FIG. 1, the register clock driver circuit 112(1) and/or the register clock driver circuit 112(2) of FIG. 1, the register clock driver circuit 312 of FIGS. 3A and 3B, the register clock driver circuit 412(1) and/or the register clock driver circuit 412(2) of FIG. 4, or any combination thereof. The first and second command and address buses and the clock signal may include the C/A A and/or the C/A B buses and the CLK signal of FIG. 1, the C/A A and/or the C/A B buses and the CLK signal of FIG. 2, the C/A bus and the CLK signal of FIGS. 3A and 3B, the C/A A and/or the C/A B buses and the CLK signal of FIG. 4, or any combination thereof.

The method 600 may include, responsive to the clock signal, providing the first subchannel command and address information to a first plurality of internal command and address connections (e.g, buses, signal lines, etc.) coupled to a first group of memories of the memory subsystem, at 630. The method 600 may include, responsive to the clock signal, providing the second subchannel command and address information to a second plurality of internal command and address connections coupled to a second group of memories of the memory subsystem, at 640. The first group of memories and/or the second group of memories may include the memories 114(1) and/or the memories 114(2) of FIG. 1, the memories 114(1) and/or the memories 114(2) of FIG. 1, the memory 314 of FIG. 3A, the memory 315 of FIG. 3B, the memories 414(1)-(16) of FIG. 4, or any combination thereof. In some examples, the first and/or the second plurality of internal command and address connections includes more than two buses. The first plurality of internal command and address connections may include the C/A A1-A4 buses of FIG. 1, the C/A A1-A4 buses of FIG. 2, the C/A bus of FIGS. 3A and 3B, the C/A A1-A2 (and A3-A4—not shown) of FIG. 4, or any combination thereof. The second plurality of internal command and address connections may include the C/A B1-B4 buses of FIG. 1, the C/A B1-B4 buses of FIG. 2, the C/A bus of FIGS. 3A and 3B, the C/A B1-B2 (and B3-B4—not shown) of FIG. 4, or any combination thereof. The first and second groups of memories include DRAM, (e.g., DDR4, DDR5, DDR6, etc.). In some examples, provision of the first subchannel command and address information to the first plurality of internal command and address connections is contemporaneous with provision of the subchannel command and address information to the second plurality of internal command and address connections.

In some examples, the method 600 may include driving, via a first driver circuit of the first (or second) register clock driver, the first (or second) subchannel command and address information to a first subset of the first (or second) plurality of internal command and address connections, and driving, via a second driver circuit of the first (or second) register clock driver, the first (or second) subchannel command and address information to a second subset of the first (or second) plurality of internal command and address connections.

In some examples, the method 600 may further include performing a first memory access operation at one of the first group of memories responsive to the first subchannel command and address information, and performing a second memory access operation at one of the second group of memories responsive to the second subchannel command and address information. The first and second memory access operations may include any memory operation, including a read or write operations.

Of course, it is to be appreciated that any one of the examples, embodiments or processes described herein may be combined with one or more other examples, embodiments and/or processes or be separated and/or performed amongst separate devices or device portions in accordance with the present systems, devices and methods.

The foregoing description of certain embodiments is merely exemplary in nature and is in no way intended to limit the scope of the disclosure or its applications or uses. In the detailed description of embodiments of the present systems and methods, reference is made to the accompanying drawings which form a part hereof, and which are shown by way of illustration specific embodiments in which the described systems and methods may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice presently disclosed systems and methods, and it is to be understood that other embodiments may be utilized and that structural and logical changes may be made without departing from the spirit and scope of the disclosure. Moreover, for the purpose of clarity, detailed descriptions of certain features will not be discussed when they would be apparent to those with skill in the art so as not to obscure the description of embodiments of the disclosure. The detailed description is therefore not to be taken in a limiting sense, and the scope of the disclosure is defined only by the appended claims

Finally, the above discussion is intended to be merely illustrative of the present system and should not be construed as limiting the appended claims to any particular embodiment or group of embodiments. Thus, while the present system has been described in particular detail with reference to exemplary embodiments, it should also be appreciated that numerous modifications and alternative embodiments may be devised by those having ordinary skill in the art without departing from the broader and intended spirit and scope of the present system as set forth in the claims that follow. Accordingly, the specification and drawings are to be regarded in an illustrative manner and are not intended to limit the scope of the appended claims. 

What is claimed is:
 1. An apparatus comprising: a first semiconductor package configured to receive first subchannel command and address information corresponding to a channel via a first command and address bus and a clock signal, the first package comprising: a first register clock driver configured to provide the first subchannel command and address information to a first internal command and address bus responsive to the clock signal; and a first memory configured to perform a memory access operation in response to the first subchannel command and address information received via the first internal command and address bus; and a second semiconductor package configured to receive second subchannel command and address information corresponding to the channel via a second command and address bus and the clock signal, the second package comprising: a second register clock driver configured to provide the second subchannel command and address information to a second internal command and address bus responsive to the clock signal; and a second memory configured to perform a memory access operation in response to the second subchannel command and address information received via the second internal command and address bus.
 2. The apparatus of claim 1, wherein the first register clock driver includes a pair of driver circuits each configured to receive the first subchannel command and address information, wherein each of the pair of driver circuits are configured to drive the first subchannel command and address information to first and second pairs of internal command and address connections that are each coupled to respective memories of the first package, including the first memory, respectively, wherein the first internal command and address bus is included in one of the first or second pair of internal command and address connections.
 3. The apparatus of claim 1, wherein the second register clock driver includes a second pair of driver circuits each configured to receive the second subchannel command and address information, wherein each of the second pair of drive circuits are configured to drive the second subchannel command and address information to third and fourth pairs of internal command and address connections that are each coupled to respective memories of the second package, including the second memory, respectively, wherein the second internal command and address bus is included in one of the third or fourth pair of internal command and address connections.
 4. The apparatus of claim 2, wherein the first semiconductor package is configured to provide a copy of the first command and address information to each of the pair of driver circuits in parallel.
 5. The apparatus of claim 1, further comprising a printed circuit board configured to mount the first semiconductor package and the second semiconductor package, wherein the printed circuit board includes a first set of traces configured to couple the first command and address bus to the first semiconductor package and a second set of traces configured to couple the second command and address bus to the second semiconductor package.
 6. The apparatus of claim 5, wherein the printed circuit board further includes a clock trace configured to couple the clock signal to both the first and second semiconductor packages.
 7. The apparatus of claim 1, wherein the first register clock driver is a first semiconductor device and the second register clock driver is a second semiconductor device.
 8. The apparatus of claim 1, wherein operation of the first register clock driver is synchronous with operation of the second register clock driver.
 9. The apparatus of claim 1, wherein the first semiconductor package is associated with a plurality of memory die each configured to receive the first command and address information from the first register clock driver.
 10. A memory subsystem comprising: a first register clock driver configured to receive first subchannel command and address information corresponding to a channel via a first command and address bus and a clock signal, wherein the first register clock driver is further configured to provide the first subchannel command and address information to a first plurality of internal command and address connections responsive to the clock signal; a second register clock driver configured to receive second subchannel command and address information corresponding to the channel via a second command and address bus and the clock signal, wherein the second register clock driver is further configured to provide the second subchannel command and address information to a second plurality of internal command and address connections responsive to the clock signal; a first group of memories configured to perform a memory access operation in response to the first subchannel command and address information received via one of the first plurality of internal command and address connections; and a second group of memories configured to perform a memory access operation in response to the first subchannel command and address information received via one of the second plurality of internal command and address connections.
 11. The memory subsystem of claim 10, wherein the first register clock driver is included in a first semiconductor device and the second register clock driver is included in a second semiconductor device.
 12. The memory subsystem of claim 10, wherein each of the first group of memories and the second group of memories includes a respective memory device.
 13. The memory subsystem of claim 10, wherein at least two of the first group of memories are included in a first memory die stack and at least two of the second group of memories are included in a second memory die stack.
 14. The memory subsystem of claim 1, further comprising a printed circuit board configured to mount the first register clock driver, the first group of memories, the second register clock driver, and the second group of memories.
 15. A method comprising: receiving, at a first register clock driver of a memory subsystem, a clock signal and, via a first command and address bus, first subchannel command and address information corresponding to a channel; receiving, at a second register clock driver of the memory subsystem, the clock signal and, via a second command and address bus, second subchannel command and address information corresponding to the channel; responsive to the clock signal, providing the first subchannel command and address information to a first plurality of internal command and address connections coupled to a first group of memories of the memory subsystem; and responsive to the clock signal, providing the second subchannel command and address information to a second plurality of internal command and address connections coupled to a second group of memories of the memory subsystem.
 16. The method of claim 15, wherein provision of the first subchannel command and address information to the first plurality of internal command and address connections is contemporaneous with provision of the second subchannel command and address information to the second plurality of internal command and address connections.
 17. The method of claim 15, furthering comprising: performing a first memory access operation at one of the first group of memories responsive to the first subchannel command and address information; and performing a second memory access operation at one of the second group of memories responsive to the second subchannel command and address information.
 18. The method of claim 15, further comprising, responsive to the clock signal: driving, via a first driver circuit of the first register clock driver, the first subchannel command and address information to a first subset of the first plurality of internal command and address connections; and driving, via a second driver circuit of the first register clock driver, the first subchannel command and address information to a second subset of the first plurality of internal command and address connections.
 19. The method of claim 15, wherein the first plurality of internal command and address connections includes more than two buses.
 20. The method of claim 15, wherein the first and second groups of memories include dynamic, random-access memories. 